Ever since the metalwood golf club burst onto the scene to replace the traditional persimmon wood, golf club designers have constantly sought to find ways to improve upon this groundbreaking design.
U.S. Pat. No. 5,474,296 to Schmidt et al. illustrate one of the earlier attempts to improve upon the design opportunity created by a hollow metalwood golf club by disclosing a golf club with a variable faceplate thickness. One way a variable faceplate thickness improves the performance of a metalwood club is by reducing the amount of weight at low stress areas of the striking faceplate to create more discretionary weight that can be placed at alternative locations in the golf club head to improve the performance of the golf club head. In addition to the above benefit, the incorporation of variable faceplate thickness can also improve upon the performance of the golf club head by adjusting the coefficient of restitution of the striking face.
U.S. Pat. No. 6,863,626 to Evans et al. illustrates this secondary benefit of adjusting the coefficient of restitution of a golf club by disclosing a golf club having a striking plate with regions of varying thickness. More specifically, U.S. Pat. No. 6,863,626 identifies this benefit by indicating that striking plate having regions of varying thickness allows for more compliance during impact with a golf ball, which in turn, could generate more ballspeed.
U.S. Pat. No. 7,137,907 to Gibbs et al. illustrates the ability to further improve upon the design of a striking face having a variable face thickness for a purpose that is different from saving weight and improving coefficient of restitution. More specifically, U.S. Pat. No. 7,137,907 illustrates a way to expand upon the “sweet spot” of a golf club head in order to conform to the rules of golf that puts a cap on the maximum coefficient of restitution allowed by a golf club. U.S. Pat. No. 7,137,907 does this by disclosing a golf club face or face insert wherein the face has an interior surface with a first thickness section and a second thickness region. The first thickness section preferably has a thickness that is at least 0.025 inch greater than the thickness of the second thickness region. The face or face insert with variable thickness allows for a face or face insert with less mass in a golf club head that conforms to the United States Golf Association regulations.
With the incorporation of variable face thickness into hollow metalwood type golf club heads, various methodologies of manufacturing have been developed to create this complicated geometry. U.S. Pat. No. 6,354,962 to Galloway et al. illustrates one methodology to create a striking wherein the face member is composed of a single piece of metal, and is preferably composed of a forged metal material, more preferably a forged titanium material. However, due to the need for precise geometry, the variable face geometry created by this conventional forging process may often exhibit waviness which will often need to be machined to the exact precise geometry. U.S. Pat. No. 7,338,388 to Schweigert et al. discusses this machining process by utilizing a ball end mill revolving about an axis generally normal to the inner surface of the face plate at an initial location on a circumferential intersection between the outer edge of the central thickened region and a transition region. The inner surface of the face plate is machined by moving the revolving ball end mill in a radial direction outwardly toward and through the transition region and the peripheral region to machine the inner surface of the face plate creating a tool channel having a width as the ball end mill traverses the transition region and thereby vary the thickness of the face plate in the tool path.
Although the machining process described above may be capable of creating a very precise geometry, the resulting striking face could still be flawed due to some inherent machining side effects. Undesirable side effects such as the existence of machine marks, circular cutting patterns, discontinuity of machine lines, starting and stopping marks, and/or machine chatters could all adversely affect the striking face.
U.S. Pat. No. 6,966,848 to Kusumoto attempts to address this issue of trying to create an improved striking face of a golf club head by disclosing a methodology wherein the stamped out face material is placed in a die assembly, wherein the face material is being thinned by causing the face material to plastically deform via pressing an upper die together with the lower die. Although this particular type of conventional forging methodology eliminates the adverse side effects of machining above described, it suffers from an entirely different set of adverse side effect. More specifically, the conventional forging of a face insert suffers from lack of material consistency and material transformation that results when a material is melted and plastically deformed resulting in grain growth and oxidation; both of which can lower the material strength of a material.
In addition to the above flaws in the current manufacturing techniques, these flaws of the current techniques become even more apparent when a designer seeks to further advance the performance of a striking face by implementing non-symmetrical geometries that would either require extensive machining, or extreme sacrifice in material property depending on the solution selected.
Hence, as it can be seen from above, despite all the attempts in addressing the consistency and accuracy issue in creating the variable face geometry in a golf club head striking face, the current art falls short in providing a methodology that can address the issues above. Ultimately, it can be seen from above that there is a need in the art for a methodology of creating the striking face portion of a golf club head with variable face geometry without relying on material conventional property changing forging techniques or simple machining techniques to ensure more precision and consistency for basic symmetrical geometries and even extreme asymmetrical geometries.